L-citrulline with HIIT alters specific microRNAs in obese older adults

BACKGROUND: High-intensity interval training (HIIT) with or without L-citrulline (CIT) oral supplementation improves body composition, functional capacities and muscle health in obese older adults, potentially through microRNA-driven regulation. We aimed to (1) investigate the impact of a 12-week HIIT on the expression level of microRNAs in vastus lateralis muscle biopsies and serum of obese older adults and (2) assess whether the differential expression level of microRNAs was associated with clinico-biological adaptations to HIIT and provide potential biomarkers of HIIT response. METHODS: In this secondary exploratory analysis of a double-blind randomized trial, 36 women and 32 men (67.2 ± 5.2 years) following 12 weeks HIIT randomized in two groups were supplemented daily with CIT (HIIT-CIT, n = 37) or with placebo (HIIT-PLA, n = 31). Phenotypic variables, serum parameters, muscle biopsies and subcutaneous abdominal adipose tissue outcomes were collected pre-intervention and postintervention. To assess the microRNA profile, the miRNome of muscle biopsy and serum was analysed using next generation sequencing in participants' subsets (n = 13). The microRNAs' differential expression level was analysed pre-intervention and postintervention by TaqMan-real-time qPCR in 68 participants. RESULTS: The expression of myo-microRNAs (miR-133a, b, -1, -206) and muscle-related-microRNAs (miR-499, -208) was not altered following HIIT with or without CIT. In HIIT-PLA, HIIT-CIT and subgroups (based on sex, age, body mass index, dynapenic status), the change in muscle (miR-504-5p, -744-5p, -151a-3p, -106b-5p, -127-5p) and circulating (miR-4433b-5p, 151a-3p, -744-5p, 483-3p, -106b-5p, -484) microRNA levels was associated with changes of clinico-biological parameters. Supplementing HIIT with CIT decreased the muscle miR-504-5p level (p = 0.022), correlating with lower body fat, improved functional capacities, muscle power and increased IGF-1 level (r = -0.6, p < 0.05). MiR-744-5p expression increased in dynapenic participants (p = 0.04), associated with lean mass gain (r = 0.50, p < 0.05), while miR-151a-3p downregulation in men's muscle (p = 0.01) was associated with better insulin sensitivity (HOMA-IR, r = 0.57, p = 0.05). In serum, miR-151a-3p upregulation in women (p = 0.01) correlated with improved muscle power and lower circulating leptin levels, while miR-4433b-5p downregulation (p = 0.001) was linked to reduced fat mass, lean mass gain and enhanced functional capacity. The downregulation of miR-106b-5p (p = 0.05) was associated with a higher adiponectin level and a better score of the 4-m walking test (p = 0.05). CONCLUSION: HIIT did not impact the expression level of myo-microRNAs and muscle-related microRNAs but induced changes in muscle-nonspecific microRNAs in muscle biopsy and serum. Modulations of microRNAs in muscle (miR-504-5p, -744-5p) and serum (miR-151a-3p, -4433b-5p, -106b-5p) were associated with HIIT's beneficial effects, suggesting their role in the HIIT effects and their potential as candidate biomarkers for response.